Various forms of apparatus have been disclosed which have the capacity for developing muscles of the human body, including those in the following U.S. Patents:
U.S. Pat. No. 3,374,782 to C. P. Izzo, 3-26-68, disclosed a pair of separate pivotal platforms for exercising with the feet on them:
U.S. Pat. No. 3,589,720 to A. Agamian, 1-29-71, disclosed a frame or track with independently movable platforms (and hand holds on one but not on the frame);
U.S. Pat. No. 3,834,693 to L. H. Poppenberger, 9-10-74, disclosed a complex of elements in an exerciser; from the top: two pivotal rests for the feet, mounted each on a separate wheeled carrier, then those on another wheeled carrier and finally a frame on a pivotal base assembly.